Band in the negative control

I keep having a product in my negative control (RT-PCR and real-time PCR) of the exact size/thermic behaviour that I am expecting in the template amplification although I changed all the solutions and the primers. The primers were tested against hairpin formations and primer dimer formations. When in the positive I have a low concentration of template, the band appears only in the negative.
With other pairs of primers I don't have the band in the negative but I don't have it in the positive as well although they are all gene specific primers.
Somebody please give me a clue or at least tell me that I'm not alone!!
Thanks